Signaling system for railroads



June 28, 1938. N. D. PRESTON SIGNALING SYSTEM FOR RAILRCADS Filed Aug.24, 1935 3 Sheets-Sheet l N. D. PRESTON SIGNALING SYSTEM FOR RAILROADSJune 28, 1938.

a SheetS-Sheet 2 Filed Aug. 24, 1935 June 28, 1938. N. 1:. PRESTONSIGNALING SYSTEM FORRAILROADS Filed Aug. 24, 1935 3 Sheets-Sheet 3 imw mPatented June 28, 1938 UNITED STATES PATENT DFFECE SIGNALING SYSTEM FORRAILROADS Application August 24, 1935, Serial No. 37,744

24 Claims.

This invention relates to signaling systems for railroads of theso-called coded track circuit type, and more particularly to a codedtrack circuit system in which the coding equipment is normally inactive,but is automatically set into operation upon the approach of a train.

In the so-called coded track circuit type of block signaling, cabsignaling, or train control system, the track circuit is intermittentlyenergized,

10 causing intermittent energization of the track relay; and it isdesirable to avoid continuous operation of relay contacts and othermoving parts employed in connection with such intermittent energizationor coding of the track circuit, un-

115 less a train is present to make it necessary to control theindications of Wayside signals or the rail current for cab signaling ortrain control purposes.

Generally speaking, and without attempting to 20 define the nature andscope of the present invention, it is proposed to provide a simple andeffective organization of relays and circuits for initiating operationof the coding and decoding equipment associated with several blocks uponthe ap- 25 proach of a train, with a minimum number of line wires, or bythe use of track rails alone without any line wires.

Various characteristic features, attributes, and advantages of theinvention will be in part ap- -30 parent, and in part pointed out as thedescription progresses.

I In the accompanying drawings, Fig. 1 illustrates in a simplified anddiagrammatic manner one embodiment of the invention employing one 35line circuit for each block for approach control;

Fig. 2 illustrates a modified organization in which, the approachcontrol is obtained by current impulses conducted over the track railsand without line wires; and

40 Fig. 3 is a diagram or chart of an explanatory character tofacilitate the explanation and understanding of the sequence of relayoperations for the modification of Fig. 2.

Referring to the drawings, the track rails 5 are 45 bonded together inthe usual Way and divided by insulated joints 6 into track sections, itbeing assumed for simplicity that these track sections will be longenough to constitute the usual block, although the same principles maybe applied to 5 blocks consisting of two or more separate tracksections.

Considering briefly the organization of parts associated with each blockin accordance with this invention, certain corresponding devices for 55the three blocks l, 2 and 3 shown are given corresponding prefixnumbers. A code following track relay T of a suitable type is connectedacross the track rails at the entrance end of the block (the normaldirection of trafiic being from left to right as indicated by thearrow). This track relay T operates suitable decoding means toselectively energize code responsive or decoder relays R'l5 and RI 841.This decoding means may take any suitable form, but as shown comprises atransformer H], with its primary having a mid 10 tap connected to oneterminal of a suitable source of direct current, the terminals of saidprimary being connected to the other terminal of the same source throughfront and back contacts ll of the track relay T. The two secondaries ofthe transformer Iii are connected through a double wave rectifier l2 tothe respective decoder relays R15 and RlBfl, with condensers IS, with orwithout additional reactance coils,

in the in-put circuits of these rectifiers proportioned to allow themaximum uni-directional current for the energization of the decoderrelays to flow when the track relay T is energized and deenergized atthe rate of 75 and 180 times per minute, respectively, all in a mannercharacteristic of decoding means of this type, and as shown anddescribed, for example, in the patent to W. D. Hailes, No. 1,852,409,April 5, 1932, for a locomotive equipment. I

The decoder relays R75 and RIM control the indications of the waysideblock signal at the entrance to the corresponding wayside block, suchsignals G of the color light type being illustrated, with controlcircuits governed by front and back contacts I4 and I5 of said decoderrelays.

Associated with each block is a modulator or coder of suitableconstruction, arranged to intermittently close contacts at the differentcode rates or periodicities; and since it is assumed that the trackcircuit is to be operated by direct current, such coder for each coderate is preferably in the form of a device having an oscillating orvibrating member operated by electromagnets energized by direct currentand actuating contacts, as distinguished from a coder driven by apolyphase or synchronous motor, such as is commonly used wherealternating current is available. One form of an oscillatory coder ofthe type contemplated is disclosed, for example, in the patent to P. N.Bossart, No, 1,858,876, May 17, 1932. For convenience in explanation, itis assumed that two code rates of '75 and 180 per minute, will be used,which however are merely typical for this purpose. These code rates areproduced by coders or modulators, diagrammatically illustrated ascomprising magnets M15 and MI 80 operating contacts C15 and C980.

At the exit end of each biock the usual track battery ['6 is connectedacross track rails 5 in series with the front contact I! of a coderepeater relay CP and the upper winding of a series relay SR. It iscontemplated that this upper winding of the relay SR will act as thelimiting resistance commonly used with primary batteries, or othersources of track circuit current having relatively negligible internalresistance. The relay SR is provided with a stick circuit including itslower winding, its own front contact l8, and the back contact I9 of thecode repeater relay CP. The relays SR also provide for approach lightingof the signals G.

In the arrangement of Fig. 1, the operation of the coders M75 and Miflflis governed by an approach control relay A of the neutral-polar typewhich is energized over a line wire 20 and a common return connectionindicated by the symbol C; and the operation of these approach controlrelays,'in conjunction with the series relays SR, provides forinitiating the operation of the coders, which are normally inactive,upon the approach oi a train.

The various circuits are shown conventionally, with the symbols andindicating connections to opposite terminals of a battery, or othersuitable source of direct current. The details of these circuitconnections are more conveniently considered in describing theoperation.

Considering now the operation of the organization shown in Fig. 1, thevarious parts are iliustrated in the normal condition when no trains arepresent. The approach control relays A are deenergized, closing thecircuits through their back contacts 2|, which may be readily traced,for maintaining the corresponding code repeater relay CP steadilyenergized, so that the track battery it of each block is continuouslyconnected across the track rails to energize steadily the code followingtrack relay T of the corresponding block. The operating characteristicsof the series relay SR are so selected or adjusted that this normaltrack circuit current, with no train present, is not sufiicienttoattract the armature of this relay. The code following track relay Tof each block being steadily energized, there is no change in thecurrent through the primary of the transformer 10, and no voltageinduced in the secondary of this transformer to energize the decoderrelays R and Rl8ll, so that both of these relays are deenergized todisplay a stop indication by lighting the red lanip R of the signal S,or in a similar way. Since the approach relay A and the series relay SR.of each block are both deenergized, their front contacts 2| and 22 areopen, and no current is applied to the coders M15 and MISBB.

Thus, under these normal conditions with no trains present, the codersare inactive, the track relays are steadily energized, and there are norelay contacts or other moving parts in operation.

In explaining how the system is set into operation upon the approach ofa train to display the proper wayside signal indications, it is assumedthat at the various places along the railroad where trains may enter theequipped territory, as at terminals, junctions and the like, there willbe a preliminary approach track section, such as the track section AP,with its usual track relay APT, located in the rear of the first signalat the entrance to the equipped territory. When a train enters suchpreliminary approach section and deenergizes track relay APT, a circuitis established over the line Wire to energize the approach relay IA forthe first block 5 of the equipped territory, the polarity of suchenergization being assumed to be so that the neutral armature 23 ofrelay A is attracted, while its polar armature is positioned to theleft. energization of relay IA closes a circuit over the line wire 20 toenergize the relay 2A for the next block 2 in advance with the oppositepolarity, such circuit being traced from C, battery 25, neutral frontcontact 23 of relay EA, polar contact 24 of relay lA to the left, backcontact 25 of series relay ISR, line wire 26, and relay 2A to Thiscircuit energizes the relay 2A to attract its neutral armature 23 andposition its polar armature to the right; but the line circuit 20 forthe next approach relay ahead is connected to the other or negativecontact of said polar armature, the next approach relay (not shown) isnot energized. In short, the entrance of a train into the preliminaryapproach section AP energizes the approach relays IA and 2A, but not anyother approach relays for blocks further ahead.

The code following track relay 3T of the block 3 being still steadilyenergized under the conditions under discussion, the decoder relay SR'JEof that block is deenergized and its back contact is closed, so thatwhen approach relay 2A is energized to close its front contact 2!, thecoder 2Ml5 for the caution code is energized, operating its.contacts2075, to intermittently energize the code repeater relay 2GP for theblock 2, the opening of back contact 2! of relay 2A breaking the circuitnormally maintaining the relay 2GP steadily energized. This applies the75 code rate to the block 2, operating its code following track relay 2Tat the same rate, which causes energization of decoder relay ZR'EE todisplay a caution indication at signal 2G. This decoder relay 2Rl'5 ofblock 2 being energized to close its front contact 30, the energizationof approach. relay iA supplies current to the coder iii H30 at the exitend of block i, which in the same manner oper ates relay ECP and iT atthe 180 code rate to energize iRltil at the entrance to block i anddisplay a proceed indication at signal iG.

Thus, when a train enters the preliminary approach section AP, assumingno trains present in biocks i or 2, the decoder relay iRifiil of theblock I is energized to display a proceed or green indication, thedecoder relay 23W block 2 is energized to display a yellow or cautionindication, and both decoder relays 31215 and ERAS!) of block 3 remaindeenergized to display a red or stop indication. In other words, when atrain enters the preliminary approach section at the entrance toequipped territory, the coding equipment is automatically started intooperation for two blocks ahead. to display a proceed indication for suchapproaching train, assuming that these two blocks are not occupied.

It will be evident, without further explana-;-

tion, that if a train should be present in block 2, its code followingtrack relay 2T would not be energized, and decoder relays 213.75 andZRiBG of that block would both be deenergized to display a stopindication, and also provide the caution 75 code rate for block i in therear to display a caution indication at signal IG at the entrance tothat block. Similarly, if a train is present in block I, the codefollowing track relay IT is not operated, and both decoder relaysii aredeenergized to display a stop indication at signal IG.

Assuming now that the approaching train in question enters block I, itswheels and axles shunt the coded current from the track relay IT, so asto give a red or stop indication at the entrance to this block. Also,the shunting effect of the wheels and axles of this train increases thecurrent through the upper winding of the series relay ESR to the extentthat this relay attracts its armature. When the relay ICP drops to cutoff the current from the battery through the upper winding of this relaylSR,

the back. contact [9 of relay lCP closes a stick circuit for holding uprelay ISR, it being desirable in this connection to make the relays SRslightly slow releasing, or adjust the back contacts I9 to make at thesame time front contacts I"! break, so that these series relays SR willnot release their armatures as the relays CP operate.

When relay ISR is thus picked up and held up by the entrance of a-traininto the block I, it closes its front contact 22 to maintain the supplyof current to coders IM15 and lMltil, even though the train later clearsthe approach section AP and relay IA is deenergized. Also, theenergization of relay lSR closes itsfront contact 26 to supply currentof opposite or negative polarity from battery M to the approach relay2A, causing its polar contact 24 to move to the left, for supplyingcurrent of polarity over the line wire it to the next approach relay(not shown) for block 3, the polar contact of such next approach controlrelay being shifted to a position where the line circuit for theapproach control relay of the next block still further in advance is notclosed. The energization of the approach control relay of block 3 startsthe coder at the end of this block to pick up decoder relay 3Rl5 forblock 3 and change the stop indication to a caution indication, in thesame manner as previously explained; and the energization of decoderrelay 3R15 of block 3 changes the code rate for block 2 to the 180 rateto change the indication of the signal at the entrance to that blockfrom caution to proceed, of course assuming that block 3 is notoccupied.

When the train in question enters block 2, series relay 2SR isenergized, and the same operation of initiating the coder for anotherblock ahead is repeated; and as the train progresses through the severalblocks the same action occurs, the coders for two blocks in advance ofthe one occupied by the train being set into operation to provide aproceed indication for such train, provided the next two blocks aheadare clear. In other words, the coding equipments are progressively setinto operation for two blocks ahead as the train advances, so that thetrain receives proceed indications so long as these two blocks ahead ofit are clear.

When a train leaves a block, the current through the series relay SR ofthat block is re duced to its normal value, and when the correspondingrelay CP is held energized, the stick circuit of relay SR is broken andthis relay releases its armature, opening its front contact 22 to stopthe coders, and remaining deenergized until the next train approaches.

The invention is illustrated as providing for the control of indicationsof wayside signals; but the same scheme of approach control of codersmay be utilized for a cab signal or train control system. In thisconnection, the front contact 22 of the series relay SR maintains inoperation the coder relay CP at the exit end of the corresponding block,even though the train has cleared the block in the rear, therebymaintaining coding of the track rail current, even though such codedcurrent is unnecessary for the purpose of controlling the indication ofthe wayside signal at the entrance to such corresponding block, thissignal indicating stop. In other words, the invention provides a schemeof approach control for maintaining a coded rail current for cab signalor train control purposes as well as governing the indications ofwayside signals. As shown the track rail current is interrupted orpulsed uni-directional current; and the locomotive equipment must beadapted to respond to such rail current, in the manner disclosed, forexample, in the patent to W. D. I-Iailes, No. 1,914,329, granted June13, 1933. If desired, alternating current of a suitable frequency, suchas cycles may be superimposed on the pulsed direct current, or in factused to energize the code following track relay through a double waverectifier, such alternating current being obtained by a local vibratoror oscillator, or from a transmission line, as convenient or desired.These and various other adaptations and applications of the inventionhave not been specifically illustrated; but it should be recognized thatthe approach control means of this invention may be utilized inconnection with various types and forms of systems employing trackwaycoding apparatus.

The embodiment of the invention shown in Fig. 1 requires line wiresextending from block to block for energization of the approach controlrelays A; and since one of the advantages of a coded track circuitsystem is the elimination of line wires for the control of signal indications, it may be considered desirable to eliminate the use of linewires even for approach con trol purposes. Such an organization forapproach control or advance starting of coding equipment without the useof line wires is shown in Fig. 2, this organization being in the natureof a modification or improvement in the system for a similar purposedisclosed and claimed in the prior application of Meyer Hormats, Ser.No. 15,646, filed April 10, 1935, no claim being made herein to subjectmatter disclosed in said Hormats application.

Referring to the modification of Fig. 2, the general organization ofcoding equipment is the same as already described, and the same seriesrelay SR is used with each track circuit; but provision is made forenergizing this series relay SR under certain conditions due to thepresence of a train in the rear, as well as by the entrance of a traininto the same block. For this purpose, an extra or supplemental battery35 is provided at the entrance end of the block, with means to connectthis battery across the track rails 5 in series with a resistance 35,when (a) the series relay SR of the next block in the rear is energizedand its front contact 31 is closed, (b) a slow acting relay SL isenergized to close its front contact 38, and (c) the decoder relay RISK]of the corresponding block is deenergized to close its back contact 39.This supplemental battery 35 is connected across the track rails with apolarity to add to the voltage of the regular track battery I6. Arectifier m of suitable construction, such as a copper-oxide rectifier,blocks the flow of current through the track relay T of the corre--sponding supplemental battery 35. The value of the resistance 36 isselected or adjusted to provide the necessary drop of potential acrossthe track rails to energize the track relay T.

The approach control function is performed in the arrangement of Fig. 2by the slow acting relay SL which, when energized and stuck up in amanner to be presently explained, opens at its back contact til thecircuit maintaining the code repeater relay CP steadily energized, andclosing at its front contact 4| the circuit for coders M15 and Mitt].This relay SL is also shown as providing approach lighting of theassociated wayside signal by closing its front contact 42, theindications of these signals being controlled by the decoder relays R15and RISE! in the same way.

The operation of the modification of Fig. 2 involves the sequentialoperation of various relays at certain time intervals; and the diagramof Fig. 3 serves to facilitate an explanation and understanding of thisoperation. It should be understood that the representations of timeintervals and the like in this diagram of Fig. 3 are merely forexplanatory and illustrative purposes, and are susceptible of suitablevariations in practice.

Considering the operation of Fig. 2, the parts are shown in the normalinactive condition with no trains present. The code repeater relays CPand track relays T are steadily energized; and the series relays SR,decoder relays R75 and RIM, and the slow acting relays SL are alldeenergized and the coders inactive.

Assuming now that the train enters the preliminary approach section AP,the dropping of track relay APT closes a line circuit, special to thisapproach section and indicated by dash lines, to energize the lowerwinding of series relay ISR for block i. This closes front contact 44 ofrelay ISR to energize relay ISL, which is stuck up through its own frontcontact 45 and front contact 46 of the track relay 2T of block 2.

This energization of relay ISL starts the coder lMl5 of block l, and atthe same time connects the supplemental battery 35 across the trackrails at the entrance to block 2, relay ISR being energized and Rltfl ofblock 2 deenergized' at this time. This picks up series relay ZSR andinturn slow acting relay ZSL, which starts the coder 2M15 at the exit endof block 2. This applies the '75 rate code to block 2, causingenergization of decoder relay 2R'i5 of block 2, which in turn starts thecoder IMBBB to supply the 180 code rate to block I.

When relay ESL is energized, it connects the supplemental battery 35 tothe block 3,, energizing 3SR (not shown), which in turn energizes arelay SSL of block 3, starting the coder 3M15 (not shown) for thatblock, which causes decoder relay 312,15 of block 3 to be energized.This starts the coder 2Ml80 of block 2, and in turn causing decoder212189 of block 2 to be energized.

When the decoder relay ZRiBll of block 2 is energized, the circuit forconnecting the supplemental battery 35 across the track rails of block 2is broken, and ZSR drops and cuts off supplemental battery 35 from block3, so that 3SR in turn drops and cuts off the supplemental battery 35for block 4. The reason relay ZSR drops is because energy is cut off itslower winding with the back contact of relay 2C]? open (relay 2GP up),during the intermittent operation of relay 2CP in response to the codebeing transmitted by coder 2Ml8il and energy in its upper winding isreduced to the drop-away value with relay 2RI80 up and its back contact39 open. Relay ZSR (and likewise other SR relays) is suiiiciently quickin releasing to drop during a period that relay ZCP is up; Relay ZSRwill not drop when 5 a train is in the associated block because onewinding or the other is always energized to the hold up value, dependingon the position of relay ZCP. While this sequential operation justdescribed is occurring, following energization of 3SL, relay 48B of thenext block 4 is energized and supplies current to relay 4SL of thatblock, but as indicated in the chart in Fig. 3, the pick up time of thisrelay 4SL is such that it does not have time to attract its armature andestablish its stick circuit before relay 4SR is deenergized and breaksthe pick-up circuit for this relay, due to the sequential building up ofthe code rates for blocks l and 2, and the sequential deenergizatio-n ofrelays ZSR and SSR.

In this connection, it should be understood that the accuracy of thetiming of the relays SL is not material to satisfactory operation; andthere may be considerable variation in the pick up times of these relaysSL, due to variations in battery voltage or the like. The slow actingrelay, such as 3SL in the case just described, for the last block aheadwhere it is needed to start the coders, must pick up before thesupplemental battery 35 is applied to the next block ahead toenergizeits relay ISR. and start the timing of its slow acting relay 4SL.Consequently, the energizing time for the relays SL may be as long asdesired, even comparable with the time taken for a train to travelthrough a block. On the other hand, if a slow acting relay, such as iSLin the case just described, is so quick in its operation as to pick upand stick before there is time for the building up of the code rates andsequential deenergizations of relays ZSR, SSH and 4SR.,, to occur, thecoding equipment will be started for one block further ahead thannecessary; but the building up of code rates and the sequentialdeenergization of relays SR will be too quick to allow two slow actingrelays 4SL and SSL to pick up in succession. In this connection, it isapparent that dash-pots, thermal elements, or other devices may beemployed to render these slow acting relays SL suificiently slow intheir operation.

Thus, by employing the track rails to energize the series relays SR, inconjunction with slow acting relays SL, entrance of a train into thepreliminary approach section and the resulting energization of the firstseries relay ISR is followed by the sequential energizations of therelays SL for three blocks in advance, initiating the coders for theseblocks and causing operation of the code following track relays anddecoding equipments in a manner to display two proceeding signals, acaution signal and a stop signal in advance of the train.

When the train in question enters the block 2, relay ZSR is againenergized by the shunting effect of the wheels and axles of this train,again;-; 55 applying the supplemental battery 35 across the track railsat the entering end of the next block 3 to energize relay 3SR, whichsimilarly causes energization of 48R, followed by energization of 4SL,starting the coder 4M'l5 (not shown) for- 7 one additional block 4ahead, and changing the code rate applied to block 3 to the next highercode rate until, when decoder relay 3RI86 is energized, the supplementalbattery 35 is disconnected from block 3, and relays 3SR, 48R and; 7

55R are deenergized successively before relay 58L has time to attractits armature, in the same manner already explained.

When the train in question leaves block I, relay ISL is deenergized,since relay I SR. drops and opens its pick-up circuit and track relay 2Tis deenergized to open its stick circuit. This restores the parts ofblock I to the normal condition, ready for the next operation.

It can be seen that the organization of Fig. 2 provides for the approachstarting of decoders for three blocks in advance of an approachingtrain, by control transmitted over the track rails and without the useof line wires. One advantage of this arrangement for starting the codersfor three blocks in advance of the train is that the coding equipment,supplying the proceed code rate to the track rails at the exit end of ablock, is in operation before the train enters that block, so that asthe train travels from block to block, the rail current for cabsignaling or train control at the high speed or proceed rate existsbefore the train enters the block, and it is not necessary to employquick starting coders, or have a time lag in the locomotive equipment toavoid receiving a restrictive indication before the proceed rail currentis established upon entering a block.

One characteristic feature of this organization of Fig. 2 is the specialprovision made, by use of a supplemental track battery 35 and therectifier 40 in series with the track relay, to obtain controlledenergization of the series relay SR. The supplemental battery 35 hassuch voltage as is necessary to obtain the satisfactory margin ofenergization of the relay SR greater than its normal energization if notrain is present; and the rectifier 40 in series with the track relayavoids improper operation of this track relay by such a supplementalbattery. The resistance 36 is necessary to provide a sufiicient voltagedrop across the track rails to energize the track relay from the regulartrack battery I6.

One outstanding attribute and advantage of a coded track circuit systemembodying this invention is that the coding equipment is normallyinactive, and there are no coders or transmitters, code following trackrelays, or other apparatus in operation while no trains are present.This obviously materially increases the useful life of apparatus of thischaracter, and is in marked contrast with a coded track circuit systemwhich is continuously operating whether trains are present or not. It isobvious that no particular useful purpose is served by having coders orcode following track relays operating at times when there are noapproaching trains to take advantage of the wayside signal indicationsor cab signaling.

If the approach control organization of this invention should, for anyreason, fail to function with respect to any particular block or blocks,such failure will not affect other blocks. The entrance of a train intoany block and resultant energization of the series relay SR willinitiate operation of the coders ahead, irrespective of what may haveoccurred previously. The use of a preliminary approach section AP isshown so that block I may be taken as part of signaled or equippedterritory; but the approach track for signaled territory may make use ofa series relay SR as the starting device, omitting relay IA and itscontrol in Fig. 1 and the energizing line circuit for [SR in Fig. 2, ina manner so obvious as not to require illustration.

The specific embodiments of the invention shown and described are merelyillustrative, and various adaptations, Variations and modifications maybe made in the specific embodiments without departing from theinvention.

What I claim is:

1. A coded track circuit system for railroads comprising, in combinationwith a track circuit having a source of current connected acrossthetrack rails at one end, a normally inactive coding device forintermittently interrupting the supply of current from said source tothe track circuit, and means including a relay in series with saidsource and between the source and the track rails for automaticallyinitiating operation of said coding device upon entrance of a train intosaid track circuit.

2. A coded track circuit system for railroads comprising, in combinationwith a plurality of track sections each having a source of currentconnected across the track rails at the exit end, a normally inactivecoding device associated with each track section for controlling thesupply of current from said source to the track rails of thecorresponding section, and means including relays in series with saidsources of current for automatically setting into operation a pluralityof said coding devices in advance of a train entering a given tracksection.

3. An. approach control system for coded track circuits comprising, incombination with a plurality of track sections each having a source oftrack rail current and a normally inactive coding device, ofelectro-responsive means for each track section connected in series withits source of current and responsive to an increase in current normallysupplied to the track rails for governing the operation of thecorresponding coding device, and means controlled by said coding devicefor governing the series connection of the correspondingelectro-responsive means with the corresponding source of current.

4. In a coded track circuit system, the combination with a plurality oftrack sections each having a source of current and a normally inactivecoding device, a series relay for each track section effectivelyenergized by an increase in the current normally supplied to the trackrails of the corresponding track section from its source, approachcontrol means for each coding device, and means including said seriesrelay for rendering effective said approach control means for aplurality of track sections in advance of a given track section occupiedby a train.

5. An approach control system for coded track circuits comprising, incombination with a plurality of track sections each having a source ofcurrent and a normally inactive coding device, an approach control relayassociated with each track section for automatically initiatingoperation of the corresponding coding device, a line circuit extendingfrom each track section to the next in advance for energizing saidapproach control relay, each approach control relay when having a givencondition of energization causing energization of the line circuit forthe approach control relay next in advance with a different condition ofenergization, a series relay associated with each track section andeffectively energized by the increase in current normally supplied tothat track section caused by the presence of a train, and means actuatedby each series relay for energizing the line circuit extending to theapproach control relay for the next track section in advance with saidgiven:

condition of energization.

6. An approach control system for coded track circuits comprising, incombination withea pluof the cprresponding coding device, a series relayfor each track section energized by the in-' crease of current normallysupplied to the track rails of that section caused by the presence of atrain, a line circuit for energizing each approach control relayextending tip the track rails next in the rear, each; approach controlrelay when energized, with 2;; given polarity causing energization ofsaid line circuit for the approach controlrelay next in advance with theopposite polarity, and means actuated by each of said series relays forenergizing the line circuit extending to the approach control relay nextin advance with said given polarity. 1

7. An approach control system for coded track circuits comprising, incombination with a series of track sections each leaving a source ofcurrent and a normally inactive coding device for controlling the supplyof current to the track rails of the corresponding section from saidsource to conform with distinctive codes, a relay for each track sectionin series with its source of current and efiectively energized by theincrease in current normally supplied to the track rails caused by thepresence of a train, said relay when effectively energizedautomatically'initiating operation of the corresponding coding device,and a stick circuit for each of said relays controlled by thecorresponding coding device for maintaining said relay energized whilesaid source of current is disconnected from the track rails.

8. In a system of the character described, a track circuit section, asource of track current, a coding device having a contact intermittentlyopened and closed, a Series relay, a circuit connecting said source ofcurrent across the track rails at one end of said track circuit andincluding in series'said contact of said coding device and said seriesrelay, a stick circuit for saidsseries relay including its own frontcontact, and means governed by said coding device for closing said stickcircuit only while said contact is open.

9. In a system of the character described, a plurality of track sectionseach having a source of track rail; current, a marginal series relay foreach track section effectively energized only by a predeterminedincrease in the current above that normally supplied to the track railsof that track section when not occupied by Ea train, and means governedby each series relay for causing effective energization over the trackrails of the series relay of the next track section in advance.

10. A system of approach control for coded track circuits comprising, incombination with a plurality of track sections each having a source ofcurrent and a normally inactive coding device, a series relay for eachtrack section effectively energized by an increase in thecurrent'normally supplied to the track rails of that section, ap-

proach control means for each track section governed by thecorresponding series relay. for initiating operation of thecorresponding coding device, said approach control means when actuatedcausing effective energization over the track rails of the series relayfor the next track section in advance, and decoding means associated.with each track section for controlling the code produced by the codingdevice of the track section next in the rear, said decoding means ofeach track section when responding to a predetermined code renderingsaid approach control means of the next track section in the rearineffective to control the series relay of the track section next inadvance of said next track section in the rear. ,7 I

11. An approach control system for coded track circuits comprising, incombination with a plurality of track sections each having a source oftrack circuit current and aenormally inactive coding device, a seriesrelay for each track section effectively energized by an increase in thecurrent normally supplied to the track rails of that track section, atime element device operated aften a time following the energization ofeach series relay for automatically initiating operation ofthe-corresponding coding device, approach control means renderedeffective by operation of said time element device for causing effectiveenergization over the; track rails of the series relay for the nexttrack section in advance, and decoding means for each track sectiongoverning the code delivered to the next track section in the rear byits coding device, said decoding means of a given track section whenresponding to a predetermined code automatically rendering ineffectivesaid approach control means governed by the time element device, of thetrack section next in the rear.

12. In a system of approach control for coded track circuits, a seriesrelay for each track section effectively energized by a predeterminedincrease in the current normally supplied to that track section when notoccupied, means governed by each series relay for causing efiectiveenergization over the track rails of the series relay for the next tracksection in advance, a normally inactive coding device associated witheach track section, and means including said series relays forautomatically initiating operation of said coding device for the firsttwo track sections in advance of a track section occupied by'a train? 1I e i '13. A track circuit for railroads comprising, a first source ofcurrent connected across the track rails at one end, a series relayconnected in series with said first source and effectively energized bya predetermined increase in the current normally supplied from saidsource to the track rails, a second source of current, means for attimes connecting said second source of current across the track. railsat the other end of said track circuit to act cumulatively with saidfirst source and thereby cause effective energization of said seriesrelay, 9. track relay, and means blocking the flow of current throughsaid track relay from said second source.

14. A track circuit for railroads comprising,

track circuit, said separate source acting cumu-Q latively with saidtrack battery Ito increase the current through said rela a resistance inseries with said separate source, a track relay, and a rectifierblocking the flow of current through said track relay from said separatesource.

15. In' a system of the character described;

means for communicating approach control in advance of a traincomprising; in combination with a plurality of track sections eachhaving a track battery connected across the track rails at the exit endand a track relay connected across the track rails at the entering end,a series relay in series with each track battery and effectivelyenergized only when the current normally supplied to the track sectionwhen not occupied is increased to a predetermined degree, meanscontrolled by each series relay for connecting a supplemental batteryacross the track rails at the entering end of the next track section inadvance to cause efi'ective energization of the series relay of thatadvance track section, and decoding means governed by each track relayfor rendering inefiective the control of the series relay of its tracksection by the series relay of the track section next in the rear.

16. A system of approach control for coded track circuits in which arelay in series with the source of current for each track section iseffectively energized by the presence of a train in that track section,means controlled by each relay for effectively energizing the seriesrelay of the track section next in advance, and means for renderingineffective such efiective energization of an advance series relay bythe one in the rear when a proceed code is transmitted to the enteringend of such advance section.

17. In combination, a stretch of railway track divided into sections,means for supplying train control current to a plurality of saidsections in sequential order when a train enters the first section ofsaid plurality, timing means for measuring off a predetermined intervalof time following the entrance of said train into said first section,and means controlled by said timing means for determining the number ofsaid sections to which said train control current is supplied.

18. In combination, a stretch of railway track divided into sections,means for supplying train control current to a plurality ofsaidsec-tions from a separate source of current at each section insequential order when a train enters the first section of saidplurality, timing means controlled from said separate sources of currentfor measuring ofi a predetermined interval of time following theentrance of said train into said first section, and means controlled bysaid timing means for determining the number of said sections to whichsaid train control current is supplied.

19. In combination, a stretch of railway track divided into sections, aplurality of control relays sequentially operated in response to theoccupancy of one of said sections, means controlled by each of saidcontrol relays for starting an associated coding device, meanscontrolled by each coding device for supplying coded track current tothe associated section, means for maintaining certain of said controlrelays operated for variable time intervals, and means controlled by thetime interval of operation of one of said control relays for determiningthe numher of said sections to which coded track current is applied.

20. In combination, a stretch of railway track divided into sections, aplurality of control relays sequentially operated by the sequentialapplication of current to said sections in response to the occupancy ofone of said sections, means controlled by each of said control relaysfor starting an associated coding device, means controlled by eachcoding device for applying coded track current to the associatedsection, means for maintaining certain of said control relays operatedfor variable time intervals, and means controlled by the time intervalof operation of one of said control relays for determining the number ofsaid sections to which coded track current is applied.

21. In combination, a stretch of railway track divided into sections, acontrol relay for each section energized from the source of trackcurrent supplied to each section when. not occupied but not picked up bysaid source of track current until the associated section is occupied,and means including a booster source of current for picking up thecontrol relay when the associated section is unoccupied.

22. In combination, a stretch of railway track divided into sections, acontrol relay for each section energized from the source of trackcurrent supplied toeach section when not occupied but not picked up bysaid source of track current until the associated section is occupied,means including a booster source of current for picking up the controlrelay when the associated section is unoccupied, and means includingcontacts of each control relay for controlling the application of saidbooster current to the next section.

23. In combination, a stretch of railway track divided into sections, atransformer energized at various rates, means responsive to theoccupancy of one of said sections for applying electrical energy to aplurality of said sections, means controlled by the number of saidsections to, which said electrical energy is applied for determining therate of energization of said transformer, and means responsive to therate of energization of said transformer for controlling the applicationof said electrical energy to said sections.

24. In combination, a track circuit, a first source of direct current, atransformer, means including said first source of current forintermittently energizing said transformer, a control circuit, means forclosing said control circuit to effect the energization of said trackcircuit from a second source of direct current, means responsive to aparticular rate of intermittent energization of said transformer foropening said control circuit, and means responsive to said closing ofsaid control circuit for efiecting the intermittent energization of saidtransformer at said particular rate.

NEIL D. PRESTON.

